Method for manufacturing permanent magnets

ABSTRACT

A method for manufacturing permanent magnets from a plurality of thin flakes of a rare earth-Fe-B alloy metal, comprising the steps of 
     subjecting the thin flakes to a discharge electric field, the thin flakes being comprised of an R-Fe-B alloy metal; and R-Fe-B-M alloy metal; an R-Fe(Co)-B alloy metal comprising 11 to 18 atom % R, 4 to 11 atom % B, 30 atom % Co, the balance being Fe; and/or an R-Fe(Co)-M-B alloy metal, 
     generating Joule heat on the contacting interfaces of the thin flakes by applying pressure to the gathered body of thin flakes and by supplying a current thereto, and 
     bonding the gathered body integrally by making the thin flakes deform plastically in a warm state. 
     R is one or more rare earth elements and M is one or more members selected from the group consisting of Si, Al, Nb, Zr, Hf, Mo, Ga, P and C. The thin flakes are in a nonequilibrium state such that the R 2  Fe 14  B phases and amorphous phases are coexistent.

FIELD OF THE INVENTION

1. Background of the Invention

The present invention relates to a method for manufacturing permanentsmagnets of arbitrary shapes using thin flakes of a rare earth-Fe-B alloymetal as a raw material.

2. Description of the Prior Art

Thin flakes of an R-Fe-B alloy metal (R indicates one or more rare earthelements) in a nonequilibrium state, as a raw material, wherein R₂ -Fe-Bphases and amorphous phases are coexistent can be obtained by rapidlyquenching an R-Fe-B alloy metal in a melted state at a quenching speedof 10⁴ ° C./sec or more and thereby, freezing at least a portion of thealloy metal in the melted state as it is. Accordingly, they are obtainedonly in such a flaky configuration having a thickness of 20 to 30 μm anda length smaller than 20 mm. Therefore, in order to form permanentmagnets of arbitrary shapes, it becomes necessary to solidify thinflakes gathered by a predetermined amount using a suitable method.

As solidifying means, there have been known a sintering method forsintering a mass of thin flakes at an ambient pressure and a hot pressmethod wherein a mass of thin flakes is pressed while being heated.

However, the conventional method such as the sintering method or the hotpress method has an disadvantage in that the magnetic properties arelowered since R₂ Fe₁₄ B phases grow too large due to a heatingtemperature higher than the crystallization temperature of the R-Fe-Balloy metal and a long heating time.

SUMMARY OF THE INVENTION

Accordingly, a main object of the present invention is to provide amanufacturing method capable of forming permanent magnets of arbitraryshapes without lowering the magnetic properties of R-Fe-B alloy metal inthe nonequilibrium state wherein R₂ Fe₁₄ B phases and amorphous phasesare coexistent.

The object of the present invention mentioned above is achieved byapplying a pressure in an axial direction to a mass of thin flakes madeof an R-Fe alloy metal, supplying an electric current thereto togenerate Joule heat at contacting interfaces among the flakes and,bonding them into one piece by making them deform plastically at a hightemperature. The Joule heat generated by supplying the current ispropagated through respective contacting interfaces and particles becomeeasy to deform plastically. Especially, atomic bonding is acceleratedregarding atoms locating on the contacting interfaces since they areeasily movable as the result of activation. Features of the presentmethod exist in that the thickness of each membrane having a largeelectric resistance is smaller than several tens nm and in the supply ofcurrent and, thereby, in that the contacting interfaces can be bonded bythe supply of current for several seconds without accompanyingtransition of the nonequilibrium state wherein R₂ Fe₁₄ B phases andamorphous phases are coexistent.

In the meanwhile, it is important and necessary for improving themagnetic properties of the R-Fe-B permanent magnet according to thepresent invention to promote rearrangement of particles upon bonding ofcontacting interfaces and to decrease vacancies by pressurizing the massof particles upon supplying the electric current.

Further, it is desirable to make contacting interfaces among particlesand/or between individual particle and a support member breakdowndielectrically by generating a discharge beforehand and, when thedischarge is caused once, surfaces of contacting interfaces are cleanedup by impacts by electrons emitted from a cathode and ions generated atan anode. And, impact pressure by the discharge can yield particlesdistortions to increase the dispersion velocity of atoms. This enablesefficient bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing a texture of solidified thin flakes ofthe permanent magnet obtained according to the preferred embodiment ofthe present invention,

FIGS. 2(a) and 2(b) are photographs showing crystal grains (R₂ Fe₁₄ Bphases) of an original thin flake and the permanent magnet,respectively,

FIGS. 3(a) and (b) are characteristic graphs showing relation among anamount (atomic %) of a rare earth element, the proper coercive force Hcjand the residual magnetic flux density Br,

FIG. 4 is a sectional view of a main part showing a composition of diesfor molding a permanent magnet.

LIST OF REFERENCE NUMERALS IN THE DRAWINGS

1 . . . Gathered body of thin flakes of a rare earth-Fe alloy metal;

2 . . . Support member of Fe;

3 . . . die of SiC;

4a . . . Punch of WC/Co;

4b . . . Punch of SiC;

5a . . . Center core of Ni base heat resistive alloy metal;

5b . . . Center core of SiC.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term "rare earth-Fe thin flake" referred to in the present inventionis a rare earth-Fe alloy metal in a nonequilibrium state wherein R₂Fe(Co)₁₄ B phases and noncrystalline phases are coexistent and can beobtained, for instance, by quenching it in a hot melted state at a veryhigh quenching speed, for example 10⁴ ° C./sec to freeze at least a partthereof in a melted state. When the single roll method is employed as aquick quenching means, the rare earth-Fe thin flakes has a thicknessfrom 20 to 30 μm ordinally. Also, in general, grain-size adjustment isdone by mechanical grinding.

A maximum value of the proper coercive force Hcj being magneticallyisotropic is obtained based on a composition of the alloy metal byconditioning the above rare earth-Fe thin flakes into a texture whereinR₂ Fe(Co)₁₄ phases of a magnitude of 40 to 400 nm are randomly gathered.

In the meanwhile, the term "conditioning" means to heat the rareearth-Fe thin flakes up to a temperature equal to or higher than thecrystallizing temperature of the R₂ Fe(Co)₁₄ B phase in an inactiveatmosphere for example Ar gas or the like and it is possible tomanufacture a magnetically anisotropic thin flakes wherein themagnetizing easy axis is oriented in a direction perpendicular to thesurface thereof when the warm rolling is employed as the heat treatment.The level of Hcj of this rare earth-Fe thin flake gives a greatinfluence on the substantial thermal stability as a permanent magnet,however, it is desirable to maintain the value of Hcj at a roomtemperature equal to or larger than 8 KOe and the size of R₂ Fe(Co)₁₄ Bphase at a value of 40 to 400 nm in order to ease factors of themanufacturing conditions, especially restrictions in the heatingtemperature. The level of the proper coercive force Hcj is fundamentallydependent on the kind of R (R is one or two or more rare earth elementsincluding Y), the amount of R and the size of R₂ Fe(Co)₁₄ B phase. Inorder to maintain Hcj equal to or larger than 8 KOe, it is desirable tomake R be Nd and/or Pr, the amount of R be a value between 12 and 15atomic % and the size of R₂ Fe(Co)₁₄ B phase be of a value between 40and 400 nm. One or two or more elements are included as substituting andadditive elements of the above rare earth-Fe thin flake and further, itis possible to include either one element or a combination of two ormore elements selected among Si, Al, Nd, Zr, Hf, Mo, Ga, P and C.Accordingly, from the view point of the composition of the alloy metalforming the rare earth metal-Fe thin flake, there are R-Fe-B,R-Fe(Co)-B, R-Fe-B-M and R-Fe(Co)-B-M alloy metals (wherein R indicatesone or two or more rare earth element and M indicates one element or acombination of two or more elements selected among Si, Al, Nd, Zr, Hf,Mo, Ga, P and C and the amount thereof is equal to or less than 3 atomic%).

The term "solidified body of rare earth metal-Fe thin flakes" indicatessuch a state in that they are directly filled into a cavity of anarbitrary shape defined by electrically conductive punches forming apair of electrodes and a die forming the cavity.

The term "direct discharge to the solidified body of rare earth metal-Fethin flakes" used in the present invention indicates to apply a directcurrent voltage and/or a low frequency voltage between the pair ofelectrode punches (0<ω<<ωpi wherein ω is a frequency of the voltage, ωpiis the frequency of an ion plasma) and to generate a discharge plasma inthe cavity.

The feature of this discharge exists in that the plasma is maintained byemission of primary electrons from the negative electrode (cathode) whengas molecules or oxidized films adhered to surfaces of the rare earth-Fethin flakes forming the solidified body in the cavity are removed by ionimpacts due to the plasma, respective thin flakes are brought into anactivated state, whereby the dispersion of atoms and the plasticdeformation tend to be generated easily. It is desirable to keep theatmosphere at a vacuum equal to or lower than 10 Torr in order to lowerthe operative pressure of the discharge plasma and to suppress surfacialoxidization of the rare earth-Fe thin flake. This is because it becomesdifficult to bring the whole of the rare earth-Fe thin flakes formingthe solidified body homogeneously into the activated state sinceconcentration of the discharge current is accelerated in an atmosphereof a high pressure since dispersion of plasma particles is suppressedtherein.

It is desirable to make application of the pressure of one axis and thecurrent referred to in the present invention at a stage in that surfacesof the rare earth-Fe thin flakes forming the solidified body in thecavity as mentioned above have been activated by the discharge plasma.Joule heat per unit volume of the solidified body of the rare earth-Fethin flakes is represented by the sum of Q_(B) =i². R_(B) (R_(B) is anelectric resistance of the contacting interface between adjacent thinflakes) and Q_(C) =i² ·R_(C) (R_(C) is an electric resistance of theinside portion of the thin flake). In general, R_(B) has a level ofabout 100 times R_(C) and therefore, if R_(B) and R_(C) are assumed toform a circuit in series, Q_(B) becomes large by about 100 times Q_(C)and, thereby, only contacting interfaces of the thin flakes are heatedmainly.

Accordingly, atomic bonding on the contacting interfaces of the thinflakes activated by the discharge plasma having been generatedbeforehand is quickly spread over the whole of the solidified body and,at the same time, gaps among the thin flakes are reduced while they aredeforming plastically.

As factors for activating the rare earth-Fe thin flakes, 1 pressure inheating 2 ion impact by the discharge and 3 movement of ions are recitedand the velocity of the atomic bonding, namely, the dispersion of atomsis represented by an equation D(δ² n/δx²)+μE(δn/δx) (wherein D:dispersion constant, n: number of dispersing particles, xi: position, μ:mobility, E: strength of electric field). Namely, the dispersionconstant D is enlarged by an amount of the internal energy increased bythe discharge and the plastic deformation and, further, dispersion ofthe ion electric field acts thereto positively. Accordingly, this isessentially superior to the hot-pressed magnet as a means forsolidifying a mass of the rare earth-Fe thin flakes by atomic bonding ata temperature equal to or higher than the crystallizing temperature.Especially, the feature of this manufacturing method is to transfer thegathered body of the rare earth-Fe thin flakes into an activated stateby utilizing a direct current (2 electrodes) discharge having been usedas a means for generating discharge plasmas and to sinter if resistivelythereafter. Accordingly, this enables not only to obtain permanentmagnets of the rare earth-Fe having arbitrary shapes very quickly butalso to suppress variations of the proper coercive force Hcj and thethermal coefficient thereof since a time needed for heating R₂ Fe(Co)₁₄B phase at a temperature equal to or higher than the crystallizingtemperature thereof can be shortened greatly and, as the result, tomaintain the thermal stability necessary for the permanent magnet.

Further, there is obtained an advantage in that an excellent magneticproperty can be obtained since partial magnetic anisotropic property inthe direction of pressure axis is enhanced by progress of the plasticdeformation. The rare earth-Fe thin flake is desirable to have anaverage particle size of a value from 53 to 250 μm. This is because theproper coercive force Hcj of the thin flake is lowered when it issmaller than 53 μm and, when it is larger than 250 μm, the resistance ofplastic deformation becomes large. Also, the pressure between electrodepunches is desirably set at a value from 200 to 250 Kgf/cm². When it issmaller than 200 Kgf/cm², the partial magnetic anisotropicalization andhigh densification by the plastic deformation become insufficient and,therefore, the proper coercive force Hcj is reduced relatively. On thecontrary to the above, even if it is set at a value higher than 500Kgf/cm², any clear improvement in the magnetic property is not observedsince the relative density becomes 99% or more at a pressure smallerthan 500 Kgf/cm2 and effects for realizing other manufacturingconditions are poor. Further, the rising temperature by Joule heatshould be kept to a temperature equal to or lower than 750 ° C. If itexceeds 750 ° C., the proper coercive force is lowered extremely by thegrowth of R₂ Fe(Co)₁₄ B phase and the plastic deformation of the thinflakes and atomic bonding of the contacting interfaces of the thinflakes have already completed sufficiently therebefore, since therelative density have reached to 99% or more already. It is sometimesadvantageous for improving an assembling property of the rare earth-Femagnet according to a variety of objects of use to cause an atomicbonding between the thin flakes and a supporting member together withthat between the thin flakes.

Hereinafter, the present invention will be explained in detail.

EMBODIMENT 1

Super-rapidly quenched rare earth-Fe thin flakes of an alloy metalcomposition Nd₁₃ Fe₈₃ B₄ were obtained by the single roll method in Aratmosphere. This thin flake was analyzed as a super-rapidly quenchedrare earth-Fe thin flake in a nonequilibrium state wherein N2Fe₁₄ Bphases and amorphous phases were coexisting. These thin flakes werefilled into a cylindrical cavity of a radius 5 mm formed a pair ofelectrode punches of WC/Co alloy metal and a die of SiC and a pressureof one axial direction and an electric current were applied to thefilled thin flakes in a direction of the height of the cavity at a roomtemperature and in Ar atmosphere. The pressure was 2 ton/cm² and thecurrent of 42 KA was supplied for 300 msec with 2 cycles from an instantdirect current source wherein discharge was done via thyrister aftercharging a current into a group of capacitors which was rectified to apredetermined voltage while rising the voltage thereof.

FIG. 1 shows a texture of solidified thin flakes of the rare earth-Fepermanent magnet having been obtained. Further, FIGS. 2(a) and 2(b) showrespective Nd₂ Fe₁₂ B crystalline particles in the original thin flakeand the rare earth-Fe permanent magnet obtained, respectively. As isapparent from the figure, atomic bonding has been caused on respectivecontact interfaces among the thin flakes and, further, vacant holes weredecreased to give a high density of relative density 98.5% sincerealignment of the thin flakes accompanied with the plastic deformationwas accelerated by applying the pressure at this stage. In addition,transition from the nonequilibrium state and generation and/or growth ofcrystalline particles of Nd₂ Fe₁₄ B layer were never caused before andafter the application of the current since the surfacial layer of thethin flake was quickly cooled by absorbing Joule heat therefrom into theinside of the thin flake.

The above rare earth-Fe permanent magnet exhibited aging properties ofBr8KG, HcB₆, 8 KOe, Hcj15KOe and (BH)max15MGOe when magnetized by pulsesof 50KOe and a high performance as a magnetically isotropic magnet wasobtained.

EMBODIMENT 2

Thin flakes of a thickness of about 20 μm was obtained by the superrapid quenching method in which a mother alloy metal of Nd₁₄.0 Co₇.5B₆.0 Fe bal melted in Ar atmosphere by the high frequency heating wassprayed onto a roll of Cu rotating at a peripheral velocity of about 50m/sec. It was confirmed by the X-ray diffraction that the thin flakeobtained was a noncrystalline thin flake having been frozen in themelted state as it was. The amorphous thin flakes were ground suitablyand particles ground were subjected to a heat treatment at 700° C. in Argas atmosphere after they were adjusted to have a particle sizes of 53to 250 μm. Thereby, super-rapidly quenched rare earth-Fe thin flakes inthe nonequilibrium state wherein Nd₂ Fe(Co)₁₄ B layers and amorphouslayer having sizes equal to or smaller than 200 nm were obtained and thethin flakes of about 20 g were filled in a cylindrical cavity of aninner radius of 20 mm. The coercive force Hcj of the thin flake at aroom temperature was 16.8 KOe. In this embodiment, the cavity wasdefined by a pair of electrode punches of graphite and a die of SiC anda pressure of 300 Kgf/cm² and a vacuum of 10⁻¹ Torr were maintained inthe cavity. Discharge plasma was generated in the cavity by applying avoltage of 30 V having a pulse width of 80 msec between the pair of theelectrode punches for an arbitrary time. Thereafter, a current supply ofabout 7.5 KVA and 2500 A was done for about 95 sec until the temperaturewas attained to 700° C. while maintaining the pressure between theelectrode punches at 300 Kgf/cm².

The, cylindrical rare earth-Fe permanent magnets of an outer radius of20 mm having various application times of the pulse voltage wereobtained by dismounting from individual cavities after cooling them downto 400° C.

Table 1 shows a relation between the application time of pulse voltage(generation time of discharge plasma) and the aging properties aftermagnetizing with pulse of 50 KOe.

                  TABLE 1                                                         ______________________________________                                        Application time                                                              of pulse voltage                                                              sec        0       15     30    60   90    120                                ______________________________________                                        Hcj, KOe   8.66    14.63  15.25 18.10                                                                              17.75 17.90                              Br, KG     8.04    8.11   8.18  8.26 8.36  8.40                               (BH)max, MGOe                                                                            13.1    14.0   14.3  15.0 15.3  15.5                               ______________________________________                                    

As is apparent from Table 1, it is very effective means for improvingeither of the coercive force Hcj, the residual magnetic flux density Brand the maximum energy product (BH)max to generate the discharge plasmain the cavity by applying a pulse voltage beforehand.

Also, compacting of the collected body in the cavity has been completedwithin a range from 680° C. to 700° C. and, therefore, the rare earth-Fepermanent magnets of arbitrary shapes can be manufactured very quickly.

EMBODIMENT 3

Super-rapidly quenched rare earth-Fe thin flakes were obtained frommother alloy metals of Nd₁₃.0 B₆.0 Fe bal, Nd₁₂.0 Co₁₆.0 B₈.0 Fe bal,Nd₁₄.0 Co₇.5 B₆.0 Fe bal and Nd₁₄.5 Co₁₆.0 B₅.5 Fe bal according to amethod similar to that of the Embodiment 2. Every about 5 g of the thinflakes was filled into each of cylindrical cavities of an inner radiusof 5 mm same as those of the Embodiment 1 and rare earth-Fe permanentmagnets of an outer radius of about 5 mm were obtained according to amethod similar to that of the Embodiment 2. In this embodiment, theapplication time of pulse voltage was kept constant, at 30 sec.

Temperature coefficients of these magnets having been magnetized by 50KOe pulses were measured by VSM and they are shown in Table 2 incomparison with that of a resin magnet having a relative density of 80%.

                  TABLE 2                                                         ______________________________________                                                    ΔBr/Br, %/°C.                                                               ΔHcj/Hcj, %/°C.                           ______________________________________                                        Nd.sub.13.0 B.sub.4.0 Fe bal                                                                -0.16 (-1.19)                                                                              -0.41 (-0.42)                                      Nd.sub.12.0 Co.sub.16.6 B.sub.6.0 Fe bal                                                    -0.1         -0.43                                              Nd.sub.14.0 Co.sub.7.5 B.sub.6.0 Fe bal                                                     -0.09        -0.39                                              Nd.sub.14.5 Co.sub.16.0 B.sub.5.5 Fe bal                                                    -0.08        -0.37                                              ______________________________________                                    

Values in brackets () are those of a resin magnet of a relative densityof 80%.

As is apparent from Table 2, the temperature coefficient of the coerciveforce Hcj falls in a range from (-0.37) to (-4.3) without exhibiting anysignificant change since the high temperature treatment can be completedin a very short time. This indicates that the thermal stability as thepermanent magnet is maintains and guaranteed together with that thelevel of the coercive force Hcj is not decreased so significantly.

EMBODIMENT 4

Ground thin flakes of a coercive force Hcj 16.5 KOe at a roomtemperature having been obtained from a mother alloy metal of Nd₁₄.0Co₇.5 B₆.0 Fe bal used in the Embodiment 2 was classified and sorted andsamples each of about 20 g having different particle sizes wereprepared.

Next, rare earth-Fe permanent magnets each of about 20 mm outer radiuswere obtained according to a method similar to that of the Embodiment 2.The application time of pulse voltage was kept constant at 30 sec.

The particle size of each sample, magnetic properties after magnetizingby 50 KOe pulses and the relative density thereof are listed up in Table3.

                  TABLE 3                                                         ______________________________________                                        particle size                                                                            32˜                                                                             53˜                                                                             106˜                                                                           150˜                                                                          250˜                            μm      53      106     150    250   300                                   ______________________________________                                        relative   97.4    99.4    99.0   98.1  93.1                                  density %                                                                     Hcj KOe    8.4     15.5    16.7   16.1  15.2                                  Br KG      6.6      8.2     8.4    8.0   7.8                                  (BH)max MGOe                                                                             8.7     14.0    15.2   13.8  12.7                                  ______________________________________                                    

As is apparent from Table 3, the residual magnetic flux density Br islowered by the reason that the coercive force Hcj is decreased when theaverage particle size becomes smaller than 53 μm and by the reason thatthe relative density is lowered when the particle size becomes largerthan 250 μm.

Accordingly, the average particle size is desirably within a range from53 to 250 μm.

EMBODIMENT 5

Super-rapidly quenched rare earth-Fe thin flakes of a coercive force Hcj17.0 KOe having been obtained from a mother alloy metal of Nd₁₄.5 Co₁₆.0B₆.0 Fe bal was obtained similarly to the Embodiment 2. Next, groundthin flakes of about 20 g were filled in a cylindrical cavity of aninner radius of about 20 mm. The cavity was formed by a pair ofelectrode punches and a die same as those of the embodiment 2 and adischarge plasma was generated in the cavity by applying a pressure of200 Kgf/cm² and a voltage of 20 V with a pulse width of 120 msec for 30sec.

Thereafter, a power supply of 2500 A: about 7.5 KVA was executed forabout 90 sec while maintaining the pressure between electrode punches at200 Kgf/cm² until the temperature of the die was raised up to 700° C.The atmosphere was set constant at an ambient pressure, 10⁻¹ Torr, 10⁻²Torr, 10⁻³ Torr and 10⁻⁴ Torr from the application of pulse voltage tothe completion of the power supply.

Table 4 shows magnetic properties of the rare earth-Fe permanent magnetshaving been magnetized by pulses of 50 KOe which were manufactured underdifferent atmospheres.

                  TABLE 4                                                         ______________________________________                                                    ambient                                                           Atmosphere Torr                                                                           pressure 10.sup.-1                                                                             10.sup.-2                                                                           10.sup.-3                                                                           10.sup.-4                            ______________________________________                                        Relative density %                                                                        94.7     99.2    99.0  99.3  99.2                                 Hcj KOe     13.2     17.2    17.4  17.3  17.2                                 Br KG        7.7      8.4     8.4   8.4   8.4                                 (BH)max MGOe                                                                              12.2     15.3    15.4  15.3  15.3                                 ______________________________________                                    

As is apparent from Table 4, it is desirable to maintain the atmosphereat a vacuum equal to or lower than 10⁻¹ Torr from the application of thepulse voltage to the completion of the current supply.

EMBODIMENT 6

Mother alloy metal of Nd₁₄ B₆ Fe bal was melted in Ar gas atmosphere bythe high frequency heating and thin flakes of a thickness 20 to 30 μmhaving coercive forces Hcj 5 KOe and 8.5 KOe were obtained by sprayingthe melted alloy metal onto a roll of Cu rotating at a peripheral speedof 50 to 80 m/sec. These thin flakes were conditioned to rare earth-Fethin flakes having coercive forces Hcj at a room temperature beingdifferent from those of the former thin flakes and every 20 g of thelatter thin flakes was filled into a cylindrical cavity of an innerradius of about 20 mm. The cavity was formed by the same pair ofelectrode punches and the die as those in the Embodiment 2 and wasmaintained at a pressure of 300 Kgf/cm² and a vacuum of 10⁻¹ Torr. Avoltage of 40 V having a pulse width of 100 msec was applied between theelectrode punches for 30 sec and, thereby, a discharge plasma wasgenerated in the cavity.

Thereafter, the pressure between the electrode punches was increased upto 500 Kgf/cm² and a current of 2500 A was supplied for about 90 secuntil temperature of the die reached to 700° C.

Table 5 shows magnetic properties of the former rare earth-Fe thinflakes and the corresponding the permanent magnets having coerciveforces at a room temperature different from each other which weremeasured after magnetizing them by pulses of 50 KOe.

                  TABLE 5                                                         ______________________________________                                        HG at a room                                                                  temperature KOe                                                                             5      8.5        12.0 14.7                                     ______________________________________                                        Hcj KOe       7.0    12.4       13.5 14.8                                     Br KG         8.3     8.6        8.5  8.5                                     (BH)max MGOe  11.0   13.4       15.4 15.6                                     ______________________________________                                    

As is apparent form Table 5, it is desirable that the coercive force ofthe rare earth-Fe thin flakes obtained by the super-rapid quenchingmethod is equal to or higher than 8.0 KOe.

EMBODIMENT 7

Seven kinds of mother metal alloys of Nd₄ B₆ Fe bal having Nd contentsdifferent from each other were melted in Ar gas atmosphere by ahigh-frequency dielectric heating and thin flakes each having athickness of about 20 μm were obtained by the super-rapid quenchingmethod wherein each of the melted alloy was sprayed onto a roll of Curotating at a peripheral speed of about 50 (M/sec). It was confirmedthat the rare earth-Fe thin flakes having different Nd contents wereamorphous thin flakes frozen in the melted stated as they were. Next,the rare earth-Fe thin flakes were suitably ground so as for particleshaving sizes ranging from 50 to 250 μm to occupy 90% or more. Next, theywere subjected to a heat treatment at a temperature of 700° C. in Ar gasatmosphere.

Thereby, rare earth-Fe thin flakes in nonequilibrium wherein Nd₂ Fe₁₄ Bphases and amorphous phases having sizes equal to or smaller than 200 nmwere coexistent in a randomly gathered state were obtained.

Every 23.5 g of samples of thin flakes having different Nd contentaccording to the super-rapid quenching method was filled into acylindrical cavity of an inner radius of about 20 mm as a collectedbody. The cavity was formed by the pair of electrode punches and the diesame as those in the Embodiment 2 and was maintained at a pressure of300 Kgf/cm² and at a vacuum of 10⁻¹ Torr using the pair of the electrodepunches. A discharge plasma was generated in the cavity by applying adirect current of 40 V having a pulse width of 50 msec for 30 sec.Thereafter, a current of 2500 A (about 7.5 KVA) was applied for about 90sec while maintaining the pressure of 300 Kgf/cm² by the pair of theelectrode punches until of the pressure axis of the electrode punchcould not be observed. A temperature at the stage that the shift of thepressure axis could not be observed was about 680° to 720° C. Next,after cooling down to 400° C., respective contents in the cavities wereremoved and, thereby, there were obtained rare earth-Fe permanentmagnets of an outer radius of about 20 mm having Nd contents differentfrom each other.

Magnetic properties at a room temperature were measured by RFM aftermagnetizing them by applying pulses of 50 KOe in a direction of thepressure axis of each of the rare earth-Fe permanent magnets havingdifferent Nd contents.

FIG. 3 is a characteristic graph showing a relation of Nd content (atom%), the coercive force Hcj and the residual magnetic flux density Brobtained from the results above mentioned. As is apparent from thefigure, both the coercive force Hcj and the residual magnetic fluxdensity Br exhibit maximum values in a range having a lower limit equalto 13 atom % of Nd content and an upper limit lower than 15 atom % ofthe same, respectively. Especially the residual magnetic flux density Bris about 8.5 KG in the range of Nd content atom % and this supports sucha result that the magnetically anisotropic cavity property was highlyenhanced in association with the partial plastic deformation of the thinflake. In the meanwhile, the temperature coefficient of the coerciveforce was measured by VSM with respect to the rare earth-Fe permanentmagnets of Nd 13 to 15 atom % after grinding those so as to have anouter radius of 5 mm and took values within a range from -0.38° to-0.40/° C.

EMBODIMENT 8

Nd of a purity of 97 wt % (the balance being other rare earth elementsincluding Co and Pr as main elements), ferro boron (purity of boronabout 20 wt %) and electrolyte iron were prepared and melted in Ar gasatmosphere by the high frequency heating so as to have a composition ofNd 29 wt %, B 1 wt % and Fe bal. Thus, an alloy metal ingot wasobtained. The alloy metal ingot was melted in Ar gas atmosphere by thehigh-frequency heating and the melted alloy metal was sprayed onto aroll of Cu rotating at a peripheral speed about 50 m/sec and a ribbonhaving a thickness of about 40 μm was obtained by the short roll method.

This ribbon was confirmed by the X-ray diffraction that it was anamorphous ribbon wherein the melted state was frozen as it was. Nd₂ Fe₁₄B phases were precipitated by hot-rolling the noncrystalline ribbon and,thereby, the thickness of the ribbon was reduced to about 20 μm. It wasconfirmed by X-ray diffraction that C axis of Nd₂ Fe₁₄ B phaseprecipitated was oriented in a direction perpendicular to the hotrolling surface. Namely, the ribbon was a rare earth-Fe magneticanisotropic strip wherein Nd₂ Fe₁₄ B phases and amorphous phases beingequal to or smaller than 400 nm were coexistent.

Next, particles obtained were filled into a cavity formed by a die ofSiC and punches of black lead and a current superposed with a directcurrent and an alternating current of 1 KHz at a ratio 5:4 was suppliedfor 30 sec while applying a pressure of one axis of 10 Kgf/cm² at firstand 300 Kgf/cm² after 5 seconds between the punches. This magnet had arelative density of 99.6% and magnetic properties thereof were theresidual magnetic flux density Br of 10.8 KG and the coercive force Hcjof 13 KOe.

In this magnet, a nonequilibrium state wherein Nd₂ Fe₁₄ B phases andamorphous phases of sizes being smaller than 500 nm were coexistent.

EMBODIMENT 9

Nd of a purity of 97 wt % (the balance being other rare earth elementsincluding Ce and Pr as main elements), ferro boron (purity of boronabout 20 wt %) and electrolyte iron were prepared and a mother alloymetal was obtained by melting them in Ar gas atmosphere using thehigh-frequency heating so as to have a composition of Nd 29 wt %, B 1 wt% and Fe bal. Next, the mother alloy metal was melted in Ar gasatmosphere by the high-frequency heating and was sprayed onto a roll ofCu rotating at a peripheral speed of about 50 m/sec.

A ribbon of a thickness of 40 μm was obtained by the single roll method.This ribbon was conformed by X-ray diffraction as an amorphous ribbonwhich was frozen in the melted state. The amorphous ribbon was subjectedto a heat treatment at 700° C. in Ar gas atmosphere and was conditionedinto a rare earth-Fe strip in a nonequilibrium state wherein R₂ Fe₁₄ Bphases and amorphous phases of sizes smaller than 200 nm were coexistentin a isometrically gathered state.

This strip was filled in a cavity of molding dies comprised of anelectrically insulating molding member, an electrically conductivemolding member and an electrically conductive support member as shown inFIG. 4.

In FIG. 4, "1" indicates a solidified body of super-rapidly quenchedrare earth-Fe thin flakes wherein R₂ Fe₁₄ B phases and amorphous phaseswere coexistent "2" indicates a support member of Fe, "3" indicates adie of SiC, "4a" indicates a punch of SiC WC/Co, "4b" indicates a punchof SiC, "5a" is a center core of a Ni base heat resistive alloy metaland "5b" indicates a center core of SiC.

Next, a current of 650 A was supplied to the conductive molding memberfor 10 sec while applying a pressure of 30 Kgf/cm² to the R-Fe-B thinflake collected body via the punches 4a nd 4b. Next, there was obtaineda structural body of permanent magnet formed as one piece from thepermanent magnetic member of 8 mm outer radius and 4 mm height and theconductive support member by removing it from the mold.

The permanent magnetic portion of the structural body of permanentmagnet had a relative density of 98.6% and was jointed to the conductivesupport member strongly.

Magnetic properties of the permanent magnetic portion cut out from thestructural body of permanent magnet were measured by VSM aftermagnetizing the same by applying pulses of 5 KOe in the radial directionthereof and were (BH)max 12.3 MGOe, Br 7.96 KG and Hcj 13.2 KOe.

In order for comparison, a ring-like resin magnet of 8 mm outer radiusand 4 mm height was prepared by injection molding Sm-Co resin magneticmaterial of injection mold grade in a radial magnetic field generated bya repulsive magnetomotive force of 40000 AT which was obtained by mixing92 wt% of Sm(Co₀.668 Cu₀.101 Fe₀.214 Zr₀.017)₇ particles of Hcj 9.8 KOeand 8 wt% of 12-polyamide of a relative viscosity 1.6 (obtained bymeasuring 0.5% m-cresol solvent at 25° C. using Ostward viscometer).After magnetizing by pulses of 45 KOe in the radial direction thereof,magnetic properties were measured. They exhibited merely (BH)max 3.7MGOe, Br 4.1 KG and Hcj 9.8 KOe.

INDUSTRIAL APPLICABILITY

As mentioned in detail, the present invention has very high industrialvalues since sintered bodies of a high density can be obtained byapplying a pressure of one axis and a current to collected body ofFe-B-R thin flakes in a nonequilibrium state.

Especially, it becomes possible to provide permanent magnets having aresidual magnetic flux density Br higher than 9 KG and a coercive forceHcj higher than 8 KOe or 15 KOe while guaranteeing excellent capabilityfor forming arbitrary shapes and productivity thereby.

We claim:
 1. A method for manufacturing permanent magnets comprising thesteps of:subjecting a gathered body of thin flakes of a rare earth-Fe-Balloy metal to a discharge electric field, said thin flakes beingcomprised of an R-Fe-B alloy metal, an R-Fe-B-M alloy metal; anR-Fe(Co)-B alloy metal comprising 11 to 18 atom % R, 4 to 11 atom % B,30 atom % Co, the balance being Fe; and/or an R-Fe(Co)-M-B alloy metal;wherein R is one or more rare earth elements and M is one or moremembers selected from the group consisting of Si, Al, Nb, Zr, Hf, Mo,Ga, P and C, and wherein said thin flakes are in a nonequilibrium statesuch that the R₂ Fe₁₄ B phases and amorphous phases are coexistent;generating Joule heat on contacting interfaces of said thin flakes byapplying pressure to said gathered body of said thin flakes and bysupplying a current thereto, and bonding said gathered body integrallyby making said thin flakes deform plastically in a warm state.
 2. Themethod for manufacturing permanent magnets as claimed in claim 1 whereinan average particle size of said thin flakes is of 53 to 250 μm.
 3. Themethod for manufacturing permanent magnets as claimed in claim 1, inwhich a size of the R₂ Fe₁₄ B phase of said thin flakes is of 40 to 400nm.
 4. The method for manufacturing permanent magnets as claimed inclaim 1 wherein said discharge electric field is a direct currentvoltage and/or an alternating current voltage of a low frequency(0<ω<<ωpi wherein ω is a frequency of said AC voltage and ωpi is anoscillation frequency of ion plasma).
 5. The method for manufacturingpermanent magnets as claimed in claim 1 wherein said discharge electricfield and the application of said pressure and said current are done inan atmosphere of a vacuum equal to or lower than 10⁻¹ Torr.
 6. Themethod for manufacturing permanent magnets as claimed in claim 1 whereinsaid pressure is larger than 200 Kgf/cm².
 7. The method formanufacturing permanent magnets as claimed in claim 1 further includingthe step of magnetizing said thin flakes anisotropically by a warmplastic deformation.
 8. The method for manufacturing permanent magnetsas claimed in claim 1 wherein the warm plastic deformation of saidgathered body of said thin flakes and said bonding between said contactinterfaces of said thin flakes are performed at a temperature lower than750° C.
 9. The method for manufacturing permanent magnets as claimed inclaim 1 wherein bonding between said thin flakes and a support member isdone at the same time of said bonding between said contacting interfacesof said thin flakes.